In recent years, porous polyimide has been researched as a separator of a lithium-ion battery, a fuel cell electrolyte film, a film for separating a gas or liquid, or a low dielectric constant material.
For example, well-known are a method for making porous by using a specific mixture solvent for a polyamide acid solution, a method for making porous by subjecting polyamide acid including a hydrophilic polymer to thermal imidization, followed by removing the hydrophilic polymer, and a method for making porous by removing silica from polyimide containing silica particles, and the like (see Patent Documents 1 to 3).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2007-211136
Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2000-044719
Patent Document 3: Japanese Unexamined Patent Application, Publication No. 2012-107144